Emission properties of Eu2+, Mn2+ in MAl2Si2O8 (M=Sr, Ba)

The emission properties of Eu2+ and Mn2+ in monoclinic SrAl2Si2O8 (M-SAS) and hexagonal BaAl2Si2O8 (H-BAS), both of which have only one alkaline-earth site, were studied. The emission peaks of both Eu2+ (405 nm) and Mn2+ (564 nm) in SrAl2Si2O8, are located at longer wavelengths, compared with those in H-BAS (373 nm for Eu2+ and 518 nm for Mn2+), because of the stronger crystal field strength at the Sr site. EPR spectra showed that the g values of Mn2+ are 4.5065 in M-SAS:Mn and 2.0247 in H-BAS:Mn. Magnetic measurements proved that Mn2+ was at high-spin state in both hosts. The large g value of Mn2+ in M-SAS was ascribed to the mixing of the first excitation state to the ground state, both of which have lower d orbital degeneracy due to the lower symmetry of Mn2+ site. The transfer efficiency from Eu2+ to Mn2+was about 10% in M-SAS, higher than that in H-BAS (5%). This was probably because Eu2+ emission overlaps the relatively low excitation level of Mn2+ in M-SAS. In order to obtain high transfer efficiency, it was necessary for the Eu2+ emission to overlap the lowest excitation level of Mn2+. The results obtained in this work may be helpful to design the new white or red phosphors for white-light emitting diode (w-LED) applications.